The present invention relates to a displacement control mechanism incorporated in a refrigerant circuit of an air-conditioning system for controlling the discharge displacement of a variable displacement type compressor, in which can change the discharge displacement varies in accordance with the pressure in the crank chamber.
In general, a displacement control mechanism includes a supply passage for connecting a crank chamber of a variable displacement type compressor with a discharge pressure region, a bleed passage for connecting the crank chamber with a suction pressure region, and a control valve for controlling the degree of opening the supply passage. The control valve controls the degree of opening the supply passage, i.e., the flow rate of refrigerant gas flowing into the crank chamber. For example, the discharge displacement of the compressor decreases as the pressure in the crank chamber increases. Conversely, the discharge displacement increases as the pressure in the crank chamber decreases.
When controlling the pressure in the crank chamber by controlling the discharge displacement of the compressor through regulation of the supply passage, as compared with controlling the discharge displacement of the compressor by controlling through regulation of the bleed passage, the discharge displacement of the compressor can be changed more rapidly since the gas in the supply passage has a higher pressure. Thus, the cooling performance of the associated air-conditioning system is improved.
For example, when the compressor is started with the refrigerant in a liquid state in the crank chamber, the liquid refrigerant in the crank chamber is discharged into the suction pressure region through the bleed passage in a liquid state and/or in an evaporated state due to, for example, a rising ambient temperature.
When changing the discharge displacement by controlling the degree of opening of the supply passage, however, a fixed restrictor is provided in the bleed passage for reducing the flow rate of the compressed refrigerant gas flowing into the suction pressure region. Therefore, upon starting the compressor, the discharge of the liquid refrigerant from the crank chamber through the bleed passage is relatively slow. As a result, a considerable part of the liquid refrigerant may be evaporated in the crank chamber, which may excessively increase in the pressure in the crank chamber. This extends the time from when the control valve closes the supply passage until the discharge displacement of the compressor starts to increase. In other words, cooling is delayed.
It is an object of the present invention to provide a displacement control mechanism for variable displacement type compressors wherein air-conditioning systems can be started with rapid cooling performance.
To attain the above object, the present invention provides a displacement control mechanism used for a variable displacement type compressor. The displacement of which varies in accordance with the pressure of a crank chamber. The control mechanism is installed in a refrigerant circuit. The refrigerant circuit includes a suction pressure zone and a discharge pressure zone. The compressor has a bleed passage, which connects the crank chamber to the suction pressure zone, and a supply passage, which connects the crank chamber to the discharge pressure zone. One of the bleed passage and the supply passage is a control passage that connects the crank chamber to a zone in which the pressure is different from the pressure of the crank chamber. The other is a regulating passage. The displacement control mechanism comprises a first control valve and a second control valve. The first control valve comprises a first valve body for adjusting the opening size of the control passage. A pressure sensitive member moves in accordance with a pressure in the refrigerant circuit such that the displacement is varied to counter changes of the pressure in the refrigerant circuit. A pressure detection region is located in the control passage. The pressure detection region is located downstream of the first valve body. The second control valve includes a second valve body for adjusting the opening size of the regulating passage. The second valve body moves in accordance with the pressure of the pressure detection region. When the pressure of the pressure detection region increases, the second control valve decreases the opening size of the control passage.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.